Antenna system having beam control members consisting of array of spiral elements



537 @ENNMN NMMM July 17, 1962 sTo 3,045,237

ANTENNA SYSTEM HAVING BEAM CONTROL MEMBERS CONSISTING OF ARRAY OF SPIRALELEMENTS Filed Dec. 1'7, 1958 4 Sheets-Sheet 1 BALANCED TRANSMISSION uNE42 EIEEFEL l ZBZ T$P|RAL ANTENNA L LENS SYSTEM SPIRAL ANTENNA ELEMENTGROU FREQ 4o OPERAUVE BALANCED DEVICE UNB CON ALANC VERTER --U ,sPmALANTENNA ELEMENTS ARTHUR E. MARSTON IEIJEILE ANOTHER VIEW OF THE LENS BYMm wwwu ATTORNEY v.1; Mminnx y 1962 A. E. MARSTON 3,045,237

ANTENNA SYSTEM HAVING BEAM CONTROL MEMBERS CONSISTING 0F ARRAY OFSPIRAL. ELEMENTS Filed Dec. 17, 1958 4 Sheets-Sheet 2 A SPIRAL ANTENNAELEMENT TRANSMISSION LINE SPIRAL GROUND ANTENNA PLANE ELEMENTS SIDE VIEWOF SPIRAL ANTENNA DEFLECTOR 7/ GROUND PLANE 54 LZ:I 3 5| /I 52 ITRANSMISSION LlNE I l l l l 1 RAD'O INVENTOR FREQUENCY ARTHUR E, MARSTONOPERATIVE DEVICE ATTORNEY y 1962 A. E. MARSTON 3,045,237 T ANTENNASYSTEM HAVING BEAM CONTROL MEMBERS CONSISTING OF ARRAY OF SPIRALELEMENTS Filed Dec. 17, 1958 4 Sheets-Sheet 3 TRANSMISSION L'NE OUNDPLANES SCANNING SPIRAL ANTENNA LENS DRIVE GROUND PLANES MECHAN'SMMEMBERS E515 SCANNING SPIRAL ANTENNA DEFLECTOR ROTATIONAL MECHANISM.SPIRAL ANTENNA I09 ELEMENT r I l I I I l l l INVENTOR I ARTHUR E.MARSTON l RADIO FREQUENCY OPERATIVE BY DEVICE ATTORNEY July 17, 1962 MRE], TQ 3,045,237

OF AR ANTENNA SY ING BEAM C L MEMBERS CONSIST RAY OF SFI LEMENTS FiledDec. 17, 1958 4 Sheets-Sheet 4 BALANCED TRANSMISSION LINE ]'2 SPIRALANTENNA ELEMENTS I RAL TENNA I15. 7 MENTs SPIRAL ANTENNA LEN YSTEMPLOYING A DIPOLE PRIM RA 0R BALANCED TO UNBALANCED 4 j CONVERTERGROUND PLANE TRANSMISSION SPIRAL ANTENNIZZELEMENTS GROUND PLANE IINVENTOR l ARTHUR E. MARSTON FIGURATION SENSE OF SPIRAL BY EMENTS FORTHE ANTENNA 0F FIG. I ATTORNEY United States Patent ANTENNA SYSTEMHAVING BEAM CONTROL MEMBERS CONSISTING 0F ARRAY 0F SPIRAL ELEMENTSArthur E. Marston, 718 Putnam Place, Alexandria, Va. Filed Dec. 17,1958, Ser. No. 781,171 17 Claims. (Cl. 343754) (Granted under Title 35,US. Code (1952), sec. 266) The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

This invention relates to antenna systems in general and in particularto antennas having radiation patterns of a highly directive nature.

In many applications of radio frequency energy operative devices it isdesirable to have an antenna system capable of producing a radiationpattern having a very high degree of directivity, that is, it has arelatively high response in a selected direction with very low responsein other directions. Such may be characterized as a pencil beam.Antennas normally produce such a beam by producing the equivalent of aplurality of parallel beams of energy having the same phase front. Thusthe energy of all the beams is additive on axis whereas in otherdirections it is either partially cancelling or otherwise nonadditive.The mechanism whereby a plurality of parallel beams may be produced issubject to considerable variation however the normal means is that ofemploying a plurality of elements which are spaced apart in directionsperpendicular to the desired maximum direction of response. Thus arrayscontaining many dipoles all of which are operated in specific phaserelationship are well known in the art being employed for example in lowfrequency radar systems. Such a multiple element array has numerousdisadvantages however because it is large, heavy and severely restrictedas to the frequency range that can be covered without retuning,furthermore, scanning to produce a variation in the direction of theaxis of directivity is attended by considerable difliculty.

Another scheme for controlling the directivity of radio frequency energyis to place a single radiating element on the focus of a parabolicreflector. As is well known, radio frequency energy from the radiatingelement thus placed is quite effectively directed in parallel paths. Thedirection of such paths may be readily controlled by movement of thecomplete unit of element and reflector. This arrangement althougheffective is subject to some limitation in that the reflector is itselflarge and heavy. A further possibility with such a reflector however isthe movement of merely the single radiating element through a small areto effectively produce a variation in the direction of emission of radiofrequency energy relative to the forward axis of the parabola. With sucha scheme as this however, there is a very definite limitation as to theangular variation possible because of the production of coma as avariation from the focus occurs producing a distortion of the desirednormal pencil beam and introducing substantial side lobe radiation.

A further scheme for controlled radiation is the use of a lens placed infront of a single radiating element to produce a refraction or bendingof the radio frequency energy so that the energy traveling outward fromthe effective point source of the element is collimated to effectivelyproduce a parallel beam of radio frequency energy. The lens scheme has asignificant advantage in that scanning by simple motion of the radiatingelement can produce substantial variation in the angle of the beamwithout requiring physical motion of the lens. However, the lens itselfpresents serious problems in that it is normally very heavy and bulky'even if simplifications, such "ice as the Fresnel principle, areresorted to. Such a radio frequency lens typically is of a material suchas polystyrene which introduces an inherent difiiculty in that it willflow of its own weight over a period of time. The conclusions to bedrawn from the foregoing are that except for very high frequencies wheredielectric lenses can be used to some extent, as a practical matter itis not pos sible to achieve undistorted pencil beam scanning with simplephysical motion of a light weight antenna element.

It is therefore an object of the present invention to provide an antennasystem of light weight and comparatively small physical size which canproduce beamed radio frequency energy in which the angular direction ofsuch beam can be controlled over broad angles and varied at a high rate.

Another object of the present invention is to provide an improved radiofrequency lens system.

Another object of the present invention is to provide an improved radiofrequency reflector system wherein an essentially planar reflectorsystem may be employed to produce parallel beams of radio frequencyenergy.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

FIG. 1 shows a basic spiral antenna lens system constructed inaccordance with the teachings of the present invention;

FIG. 2 shows another view of the lens of FIG. 1;

FIG. 3 shows in general the configuration of an individual spiralantenna element;

FIG. 4 shows a side view of a spiral antenna reflector constructed inaccordance with the teachings of the present invention.

FIG. 5 shows a scanning spiral antenna lens constructed in accordancewith the teachings of the present invention;

FIG. 6 shows a scanning spiral antenna reflector constructed inaccordance with the teachings of the present invention;

FIG. 7 shows a spiral antenna lens system employing a dipole primaryradiator; and

FIG. 8 shows the alternate configuration sense of the spiral elementsfor the antenna of FIG. 7.

In accordance with the basic teachings of the present invention, a radiofrequency lens or reflector is provided utilizing the properties of aspiral antenna element typified in FIG. 3 and described subsequently.One of the unique properties of a spiral antenna element is its abilityto provide control of the phase of electrical energy in the far fieldmerely by rotation of the element, one degree rotation of the elementproviding one degree phase change in the far field. Thus if the spiralantenna element is rotated through a typical 20 degrees in onedirection, the phase of the radiation field of that spiral antennaelement is altered at every point in the far field by precisely thatsame amount. Thus a plurality of spiral antenna elements are employedand adjusted in angular orientation relative to each other to produce aspecific phasing of the field produced thereby regardless of the phasingof excitation of the individual elements. It is possible therefore for aseries of spiral antenna elements to produce an outgoing phase frontwherein all elements contribute energy which is in-phase or which bearsselected relative phasing to produce in effect a beam similar to thatproduced with light by an optical lens. Unlike the optical lens,however, this particular configuration is characterized by an ability toalter the efiective direction of emission of energy by variation of thephase front to produce scanning.

With reference now to FIG. 1 of the drawing, the

apparatus shown therein contains a first spiral antenna element which iscoupled through a coaxial cable 11 and a balance to unbalanced converter12 to a radio frequency operative device 13. The radio frequency energyoperative device 13 could be a receiver for reception purposes as wellas a transmitter to excite the antenna system for emission of radiofrequency energy.

The element 10 which provides inherently a broad pencil beam on bothsides is backed by a suitable ground plane 14 which serves to confinethe radiation to one direction, typically toward the right in FIG. 1. Inthis direction relative to element 10 is a group of elements 15-23.Elements 15-23 are connected by means of balanced transmission lines24-32 to a second group of elements 33-41. The groups of elements aretypically separated by approximately one-half wavelength with a groundplane 42 placed between, the transmission lines 24-32 passing throughsuitable apertures in the ground plane 42.

A specific relationship between the configuration senses of the variouselements is important to secure the foregoing result. Thus element 10has typically a right hand configuration sense when viewed from thedirection of the elements 15-23 in which case the elements 15-23 wouldalso have a right hand configuration sense when viewed from the element10. This insures coupling between the element 10 and the elements 15-23.Furthermore, the elements 33-41 will be of a left hand configurationsense when viewed from a direction looking toward the ground plane 42.

FIG. 2 indicates in a general way a typical rectangular layout of spiralantenna elements and ground plane 42 as viewed typically in thedirection of ground plane 42 from the side on which the elements 33-41are disposed. Thus the array is seen to have depth as well as heightproviding a high degree of directivity in both planes. In thosesituations where a greater degree of directivity is desired in one planethan in another it is of course obvious that more antenna elements couldbe employed in one plane than in the other.

The operation of the apparatus of FIGS. 1 and 2 is as follows, forsimplicity of explanation the device being described in terms of atransmitter rather than a receiver, however, it is to be understood thatthe device is usable for reception as well as transmission. Radiofrequency energy produced by the radio frequency operative device 13 isdelivered by way of the feed line 11 through the balanced to unbalancedconverter 12 where it is fed antiphase to the two conductors of theelement 10. Element 10 provides a broad pencil beam in the directiontoward the right in FIG. 1 so that radio frequency energy emittedthereby reaches the elements 15-23 but does not proceed beyond theground plane 42. The radio frequency energy intercepted by elements15-23 is delivered by corresponding transmission lines 24-32 to elements33-41. Elements 33-41 are thus energized to produce a broad pencil beamwhich is confined to the right direction in FIG. 1 by the ground plane42. With each of the spiral antenna elements '33 through 41 assumed forthe present to be radiating in-phase, it is thus seen that the energytraveling in the right direction of FIG. 1 will be additive for allantennas so that a narrow pencil beam will be the overall result of thecomplete array.

Control of the phasing of the energy emitted by each of the elements33-41 is effected merely by rotation of each of the elements about itsaxis perpendicular to the plane of the spiral conductors. Thus each ofthe elements will be rotated by a selected amount to produce the desiredphase shift in the overall path of energy through each of the elements.Thus typically, elements 19 and 37 would be rotated together by aselected amount to place them in a selected initial phase and otherelements would be rotated as required to achieve the selected phaseshift. This status could be preserved or, if scanning is desired,altered by suitable means 9 Ell the phase of the energy transmittedthrough the element pairs. As has been stated, it is characteristic ofthe spiral antenna that physical rotation thereof about the axisperpendicular to the plane of the spiral produces a phase change in thefar field which is equal in the number of degrees to the angularitythrough which the element is rotated. Thus, if the element is rotatedthrough a typical 45 degrees the phase in the far field is altered bythe same 45 degrees. Where two elements, typically 19 and 37, areconnected together as in FIG. 1 and rotated as a unit through a givenangle, the net change in the phase in the far field is twice the amountof angular rotation of the unit provided the elements are arranged withconfiguration senses as described in FIG. 1. Thus rotation of the unitconsisting of elements 19, 37 through a typical angle of 45 degreeswould cause a phase change of 90 degrees in the far field produced byantenna 37.

In accordance with the basic principles thus set forth it is seen thatthe exact lengths of the transmission lines 24-32 are not critical norare the lengths between the element 10 and the elements 15-23, sincemerely by initial rotation of the various elements 15-23 and 33-41 it ispossible to control the phasing of the energy emitted thereby to wherethe desired in-phase condition may be obtained to produce the pencilbeam radiation pattern.

It is further a property of the apparatus of FIG. 1 that once theelements are set up to produce in-phase radiation in the far field sothat a narrow pencil beam is produced, the direction of the narrowpencil beam may be varied over a wide angle without distortion of thebeam merely by rotation of the individual elements. This rotation,although of a very simple nature which can be easily accomplished byelectrical or mechanical drive means or merely by the manual positioningof the elements, must be done according to a prescribed pattern which isdescribed in the following. Typically to produce a shift of the patternin the upward direction each of the elements displaced from the centralelement must be rotated through precise relative angles, typicallyelements 19 and 37 would not be rotated whereas the paired elements 18and 36 would be rotated in one direction through an angle 6, elements 17and 35 would be rotated in the same direction through an angle 20,elements 16 and 34 would be rotated in the same direction through anangle 30, and so forth. Elements on the opposite side of the elements 19and 37 would be rotated in the opposite direction, for example 20 and 38would be rotated through an angle 0, elements 21 and 39 through an angle20, elements 22 and 30 through an angle 30, etc. To produce a shift ofthe direction of the beam in the opposite direction, the above directionof angularity of rotation of the various elements need merely bereversed. With such an antenna array as the foregoing it is readilypossible to move the antenna directivity pattern through an angle of 45degrees in each direction or a total of 90 degrees in each plane withoutany serious distortion of the basic narrow pencil beam pattern. Astypical examples of the value of 0 to produce a given angulardisplacement of the beam, the beam will be displaced by an angle whichis approximately where 6 is the basic rotation of the first displacedpairs of elements 18 and 36, 20 and 38.

In summary therefore with regard to FIGS. 1 and 2, it is seen that anarray is provided having for all practical purposes the properties of alens since merely by rotation of the various spiral antenna elementsconstituting the array in accordance with basic principles set forthabove it is possible to produce desired phasing of the energy leavingthe elements 33-41. It is thus possible to simulate a lens of a desiredrefractive power as well as a desired area to produce a beam of desiredsharpness. Such a lens is of considerable value in such diverse fieldsas radar and radio astronomy.

The spiral antenna element indicated more or less schematically in FIG.3 appears to behave as if it were a two wire transmission line whichgradually by virtue of its spiral geometry transforms itself into aradiating structure or antenna. A spiral antenna element as typified inFIG. 3 is a planar assembly consisting of two interspaced conductorsdisposed layer upon layer in such a manner as to present a spiralconfiguration having a first or a second sense depending upon whetherthe outward spiral from the center is in a clockwise orcounter-clockwise direction. For example, the two conductors could beprinted circuit conductors disposed on a base member or disc ofnon-conductive supporting material. Each conductor has a starting pointnear the center of the disc and a termination near the periphery of thedisc, the terminations of the two conductors occurring at diametri callyopposed portions of the periphery. Such a spiral antenna element may beenergized at the center by means of a balanced feed system or a coaxialcable with one conductor of the coaxial cable connected to one conductorof the element and the other conductor of the coaxial cable connected tothe second conductor of the element. In such a coaxial cable arrangementhowever it is ordinarily desired that a balanced to unbalanced converterbe inserted between the element conductors and the coaxial cable. Whensuch an element is energized by radio frequency energy it radiates abroad circularly polarized pencil beam to each side of the plane of theelement. Each radiated beam is normal to the plane of the element andthe sense of circularity of polarization of the beam on any one sidecorresponds to the winding sense of the element as viewed from theopposite side. Accordingly, the two radiated beams are substantially thesame except that the sense of polarization of the radiated field on oneside is the opposite of that on the other. In many applications such aswith the elements of the present invention it is desirable that theelements radiate to one side only, such being readily accomplished byappropriately backing the elements on one side with a ground plane toproduce reflection of energy, or with a cavity to produce absorption ofenergy. Where a ground plane is used it is normally preferable to spaceeach element and the ground plane apart by a distance equal toa quarterwavelength or an odd multiple thereof, thus, in-phase reflection occurs.

Although the exact theory of operation of the spiral antenna is notrigorously established at the present time, I a possible explanation isthat each spiral antenna element behaves as if it were a two wiretransmission line which gradually by virtue of its spiral geometrytransforms itself into a radiating structure or antenna. Ordinarily atwo wire transmission line wherein the wire spacing is a small fractionof a wavelength yields a wholly negligible amount of radiation whenexcited at its terminals. This is due to the fact that currents in thetwo wires of the line at any normal cross-section are 180 out of phaseso that the radiation from one line is essentially cancelled by theradiation from the other. In such an antenna element as that shown inFIG. 3, if the spacing between adjacent conductors is substantiallysmaller than the radius of the outer turn of the element, the differencein length between the two conductors from-the origin to a point in theoutermost circle is approximately equal to half the circumference of theelement. With anti-phase excitation of the conductors at the center, thephasing gradually changes along the length of the two conductorsproceeding outwardly so that where the radius of the outer conductor isthe currents in the two conductors are precisely in-phase and radiationis at a maximum. Such a spiral antenna element when excited at higherfrequencies wherein the outer conductor radius is greater than wouldachieve such an in-phase condition at a smaller radius than theperiphery so that portions of the conductors located at the smallerradius produce maximum radiation. Such an antenna thus is characterizedby wide band operation with respect to frequency because selectedportions thereof become elfective at different portions of the frequencyband.

With reference now to FIG. 4 of the drawing, the lens principles of FIG.1 are shown applied to a reflector. The apparatus shown thereincomprises a radio frequency operative device 50 which as previouslyindicated can be a transmitter or a receiver, the explanation whichfollows being more easily carried out by speaking of device 50 as atransmitter. The radio frequency operative device 50 is connected tospiral antenna element 51 by means of a coaxial cable 52 preferablythrough a balanced to unbalanced converter 53. As before the element 51is backed by a suitable ground plane device 54 which typically is spacedtherefrom by a quarter wavelength. Disposed in front of element 51 are aplurality of spiral antenna elements 55-63. Spiral antenna elements55-63 are spaced a quarter wavelength from and supported by a groundplane member 64. The supports of the elements are numbered 65-73 and inaddition to providing support of the elements are also balancedtransmission lines terminated in a short circuit which are thuspurposefully made reflective. Thus energy intercepted by the elements55-63 travels down the transmission lines 65-73, is reflected by theshort circuit from which it travels back to the elements 55-63 and isreradiated. In accordance with the basic principles outlined inconnection with FIG. 1, the elements 55-63 may be oriented with carefulattention to the angular phasing thereof as determined by the positionof the conductors of the elements so that positive control of the phaseof the energy reradiated by each element is possible. To apply theprinciples of FIG. 1 however requires attention to certain details andprinciples. Thus to permit the elements 55-63 to couple to the element51, attention to configuration sense is required, in that element 51 andelements 55-63 must have the same configuration sense.

The operation of FIG. 4 apparatus may thus be summarized as thereradiation of energy emitted by a point source, such reradiationoccurring with a selected control of phasing of the energy so that theoutgoing or reradiated energy from each element has a selected phase.Typically where all of the energy is emitted in the same phase a narrowpencil beam will result in a direction perpendicular to the elements55-63. As before, the direction of this pencil beam may be controlled orvaried by proper relative rotation of the individual spiral elements sothat any degree of angularity within the limits of the beam of theindividual antenna elements may be obtained.

FIG. 5 shows an arrangement of apparatus utilizing the basic lensstructure of FIG. 1 with lengthened transmission lines -83, and twoground planes 84, having a finite spacing to allow the insertion of adrive mechanism 86 to provide programmed rotation of the individualspiral antenna elements in forward and reverse directions and in desiredrelative angular rates as set forth in connection with FIG. 1. Drivemechanism 86 could simply be a suitable set of gearing utilizing wellknown ratio principles to provide the angular relationships plus andminus 0, 20, 30, etc., discussed in connection with FIG. 1. It isunderstood of course that angular variations in both directions of FIG.2 would be necessary to produce scanning of the output beam in thetypical azimuth and elevation planes. Thus radiation from the completeapparatus of FIG. 5 would be in a direction generally corresponding tothat indicated to the right in FIG. 5 by arrow 87 whereas it could alsobe caused to be displaced therefrom in any direction typically asindicated by arrow 88 by the rotation of the individual 7 spiral antennaelement pairs according to principles previously set forth.

FIG. 6 shows an extension and combination of the principles enumeratedin connection with the reflector of FIG. 4 and the lens of FIG. 5. Adrive mechanism 89 is placed in back of the ground plane 90 and themembers 91 through 99 are extended at least as far as the mechanicalportions thereof are concerned to provide programmed orientation of thespiral antenna elements 100-108 to produce control of the direction ofthe pencil beam of the array. Thus scanning can be obtained with theelement 109 held in a fixed position and the various antenna elements100-108 rotated through plus or minus angles in the relationship of 0,20, 30, etc., to produce changes in the antenna direction. It is seentherefore that a large structure employing many hundreds or more ofspiral antenna elements may be mounted with a suitable ground plane 90and a rotational mechanism 89 to provide a device for radio astronomywithout requiring any complicated supporting structure or rotatingmechanism to position a huge, weighty, parabolic reflector.

Thus far the invention has been described with spiral antenna elementsas the basic feed, 10, 51, 109 to facilitate an understanding of thecoupling of the energy in the antenna systems, but with these systems,the single spiral feed results in the production of emitted energyhaving circular polarization. It is not always desirable to employcircular polarization, for example, linear polarization in one plane oranother may be desirable in certain instances. The apparatus of FIGS. 7and 8 shows the linear polarization arrangement as applied to the basicapparatus of FIGS. 1 and 2. Two differences are present, namely thespiral antenna element 10 of FIG. 1 has been replaced by a dipole 10A inFIG. 7, and all the spiral antenna elements on each side of the groundplane 42 no longer have the same configuration sense, but alternate on achecker board pattern basis.

The operation of the antenna of FIGS. 7 and 8 thus incorporate theprinciples of the spiral doublet antenna wherein the dipole 10 emitslinearly polarized energy which couples to the elements -23 regardlessof their configuration sense. Energy then couples out from each of theelements 33-41 with circular polarization however of opposite sense fromthose elements arbitrarily marked L (left hand configuration sense) thanit does from those elements having the opposite configuration sense, R.The two polarizations combine in the far field, the result being linearpolarization.

The phasing dependency of energy in the far field upon rotation of theelements is maintained however so that scanning is obtained by rotationof the elements as with the previously described devices. In generalhowever, elements marked R and L must be rotated in opposite directionsto provide scanning, thus in keeping with the previous scanning scheme,in FIGS. 7 and 8, the horizontal row including element 37 (and its mate19 on the opposite side of ground plane 42) would remain stationary, thehorizontal row including element 36 would be rotated through 0 degreesin first directions, typically clockwise, for elements marked R andcounter-clockwise for elements market L whereas the horizontal rowincluding element 38 would be rotated in opposite directions,counter-clockwise for elements marked R and clockwise for elementsmarked L, the horizontal row including element 35 through 26 inappropriate directions clockwise, etc. This would produce scanning inthe plane of the elements 33-41 with energy having polarization asdetermined by the dipole 10-A.

Likewise scanning in the plane perpendicular to the plane of elements3341 is obtained by differential rotation of the vertical rows ofelements in FIG. 8.

For the foregoing discussion the groups of spiral elements have beendescribed as being in planes and the term ground plane has been used. Itis to be understood that the principles of the present invention couldbe ap- 8 plied to arrays having a ground plane which is not a trueplane, for example, it may be an ellipsoid of revolution, in which caseadvantages may accrue from disposition of the planes of the variousspiral elements in each group in positions other than in the same plane.In such case control of the phase front is still possible by rotation ofthe individual spiral elements.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. An antenna comprising, a primary antenna element, a plurality ofsecondary antenna elements of the spiral type individually coupled tosaid primary antenna element and to space, and phase control meansconnected to the spiral antenna elements for controlling the angularorientation of the secondary antenna elements to adjust the phase shiftsof the overall transmission paths between the primary antenna elementand space through the secondary antenna elements.

2. An antenna comprising, a primary antenna element, a plurality ofsecondary antenna elements of the spiral type for providing coupling tospace, means for coupling the primary antenna element to the spacecoupling of the secondary elements and means for individually varyingphase shift introduced by each of said means for coupling, said meansincluding means for adjusting the angular orientation of the secondaryantenna elements.

3. In combination, a radio frequency operative device, a primary antennaelement coupled to said radio frequency operative device, a plurality ofsecondary antenna elements of the spiral type for providing coupling tospace, means for coupling the primary antenna element to the spacecoupling of the secondary elements and means for individually varyingphase shift introduced by each of said means for coupling, said meansincluding means for adjusting the angular orientation of the secondaryantenna elements.

4. In combination, a radio frequency operative device, a primary antennaelement coupled to said radio frequency operative device, a plurality ofsecondary antenna elements of the spiral type for providing coupling tospace, and means for coupling the primary antenna element to thesecondary elements, said means including separate phase controlapparatus for each of said secondary elements whereby selected phaseshifts can be introduced into the energy coupled between the primaryantenna element and space through said means.

5. In combination, a primary antenna, a first group of spiral antennaelements coupled to the primary antenna, a second group of spiralantenna elements disposed in a broadside array and coupled to freespace, means connecting the elements of the groups in pairs wherein eachpair contains one element from each group whereby energy received by theelements in one group can be reradiated by the elements of the othergroup and means rotatably mounting the connected elements whereby thephase of the resultant coupling between the primary antenna and freespace through the groups is adjustable.

6. A directional antenna assembly for operation with a radio frequencydevice comprising, a primary antenna, a first group of spiral antennaelements coupled to the primary antenna, a second group of spiralantenna elements disposed in a broadside array and coupled to space, aground plane interposed between the first and second groups forpreventing direct space coupling therebetween, means connecting theelements of the groups in pairs wherein each pair contains one elementfrom each group whereby energy received by the elements in one group canbe reradiated by the elements of the other group, and means forrotatably mounting the elements whereby the phase of the resultantcoupling between the primary antenna and free space through the groupsis adjustable.

7. A directional antenna assembly for a radio frequency device,comprising a primary antenna, a first group of spiral antenna elementsof one configuration sense which coupled to the primary antenna, asecond group of spiral antenna elements having a configuration sense theopposite of that of the first group disposed In a broadside array andcoupled to free space, a ground plane interposed between the first andsecond groups for preventing direct space coupling between the groupsand to the primary antenna, means connecting the elements of the groupsin pairs wherein each pair contains one element from each group wherebyenergy received by the elements in one group can be reradiated by theother group, and means for rotatably mounting the elements whereby thephase of the resultant coupling between the primary antenna and freespace through the groups is adjustable.

8. A directional antenna assembly for a radio frequency device,comprising a primary antenna having linearly polarized radiationconnected to the radio frequency device, a first group of spiral antennaelements disposed in a broadside array having alternate elements ofopposite configuration sense, a ground plane interposed between saidantenna and said elements for preventing direct coupling therebetween, asecond group of spiral antenna elements disposed in a broadside arrayhaving alternate elements of opposite configuration sense interposedbetween said ground plane and said antenna, means connecting theelements of the groups in pairs wherein each air contains an element inone group having one configuration sense and an element in the othergroup having the opposite configuration sense whereby energy received bythe elements in one group can be radiated by the other group, and meansfor rotatably mounting the elements whereby the phase of the resultantcoupling between the primary antenna and free space through the groupsis adjustable.

9. A directional antenna for a radio frequency device, comprising, aprimary antenna connected to the radio frequency device, a first groupof spiral antenna elements disposed in a broadside array havingalternate elements of opposite configuration sense, a ground planeinterposed between said antenna and said elements for preventing directcoupling therebetween, a second group of spiral antenna elementsdisposed in a broadside array having alternate elements of oppositeconfiguration sense interposed between said ground plane and saidantenna, means connecting the elements of the groups in pairs whereineach pair contains an element in one group having One configurationsense and an element in the other group having the oppositeconfiguration sense whereby energy received by the elements in one groupcan be radiated by the other group, means for rotatably mounting theelements whereby the phase of the resultant coupling between the primaryantenna and free space through the groups is adjustable, and drive meansfor varying the rotation of the elements in a selected relationship toproduce variations in the antenna directivity.

10. A directional antenna for a radio frequency device, comprising, aprimary antenna connected to the radio frequency device, a ground planedisposed on one side of said primary antenna in proximity thereto, agroup of secondary antenna elements disposed in a broadside arrayinterposed between said ground plane and said primary antenna, saidsecondary antenna elements being space coupled to said primary antenna,reradiation control means connected to each secondary antenna elementfor producing reradiation by each secondary antenna element withselected time delay after energy is incident thereon.

11. A directional antenna for a radio frequency device, comprising, aprimary antenna connected to the radio frequency device, a ground planedisposed on one side of said primary antenna in proximity thereto, agroup of spiral antenna elements disposed in a broadside arrayinterposed between said ground plane and said primary antenna, saidspiral antenna elements being space coupled to said primary antenna,reradiation control means connected to each spiral antenna element forproducing reradiation by each spiral antenna element with selected timedelay after energy is incident thereon.

12. A directional antenna for a radio frequency device, comprising, aprimary antenna connected to the radio frequency device, a ground planedisposed on one side of said primary antenna in proximity thereto, agroup of spiral antenna elements disposed in a broadside array havingalternate elements of opposite configuration sense interposed betweensaid ground plane and said primary antenna, said spiral antenna elementsbeing space coupled to said primary antenna, for reradiation controlmeans connected to each spiral antenna element for producing reradiationby each spiral antenna element with selected time delay after energy isincident thereon.

13. A directional antenna for a radio frequency device, comprising aprimary antenna connected to the radio frequency device, a ground planedisposed on one side of said primary antenna in proximity thereto, agroup of spiral antenna elements disposed in a broadside array havingalternate elements of opposite configuration sense interposed betweensaid ground plane and said primary antenna, said spiral antenna elementsbeing space coupled to said primary antenna, reradiation control meansconnected to each spiral antenna element for producing reradiation byeach spiral antenna element with selected time delay after energy isincident thereton, and means for producing relative rotation of thespiral antenna elements to control the phase of energy reradiated byeach element.

14. In combination, a radio frequency operative device, a primaryantenna element, a plurality of secondary antenna elements of the spiraltype individually coupled to said primary element and to space, andphase control means connected to the secondary antenna elements forcontrolling the angular orientation of the secondary antenna elements toadjust the phase shifts of the overall transmission paths between theprimary antenna element and space through the secondary antennaelements.

15. An antenna comprising, a primary antenna element, a plurality ofsecondary antenna elements of the spiral type disposed in a planeindividually coupled to said primary element and to space, and phasecontrol means connected to the secondary antenna elements for adjustingthe phase shifts of the overall transmission paths between the primaryantenna element and space through the secondary antenna elements.

16. A directional antenna assembly for operation with a radio frequencydevice, comprising a group of antenna elements of the spiral typecoupled to space, a primary antenna element coupled to the radiofrequency device, a second group of antenna elements of the spiral typecoupled to the primary antenna element, means connecting each of thesecond group of antenna elements to an element of the group of antennaelements whereby the radio frequency device is coupled to space, andmeans for in- .dividually varying phase shift introduced by each of saidmeans connecting, said means including means for adjustmg theorientation of at least one of the groups of elements.

17. Apparatus for providing phase coordination in the coupling of aplurality of spiral antenna elements be tween space and an energyoperative device comprising, a primary antenna element coupled to saiddevice, means for coupling the primary antenna element to the spiralantenna elements, and adjustable phase shift means for individuallycontrolling the phase shift in the coupling through each of said spiralantenna elements and means for coupling.

(References on following page) 11 12 References Cited in the file ofthis patent FOREIGN PATENTS UNITED STATES PATENTS 668,231 Germany Nov.28, 1938 2,408,373 Chu Oct. 1, 1946 OTHER REFERENCES 2461005 southworthFeb'81949 5 Ground-to-Air Antenna Uses Helical Array, Elec- 2,464,276Vanan Mar. 15, 1949 2 566 703 1am Se t 4 1951 Homes, March 1956, pages161, 162 and 163.

S p NRL Report 5103 Scanning Arrays Using the Flat 2,663,869 Adcock eta1. Dec. 22, 1953 Sp1ra1 Antenna, by Kalser, May 16, 1958. 2,736,895Cmhrane "Feb-28,1956 Aviation Week v61 62 No 2 Jul 14 1958 a es2,773,254 Englemann Dec. 4, 1956 Y P g 2,935,746 Marston May 3, 1960 1081

